On the clinotron effect in a backward-wave tube

The results of a theoretical study of the clinotron effect in a clinotron model, which takes into account static electron trajectories in the focusing magnetic field and the initial spacing between the lower beam boundary and the surface of the slow-wave structure, are presented. Physical processes of interaction between a thick electron beam with transverse dimensions comparable with the length of the slow wave and the RF field at its oblique incidence onto the structure are considered. It is demonstrated that, as the current is increased from the starting to the working value, a beam tilt is necessary to reduce the nonlinear effects of interaction between the beam and the RF field and prevent the complex self-oscillation dynamics in the clinotron; in the small amplitude mode (start), the beam tilt is related to optimization of the beam supply into the interaction space, which ensures the minimum starting current. In addition, it is shown that, in the presence of the initial spacing between the beam and structure, the reduced clinotron efficiency η/С increases and, at the optimum tilt angle, is no less than the normalized efficiency of classical backward-wave tubes with a thin electron beam.     

Following-wave amplification mode of a clinotron

The following-wave amplification mode of a model of the clinotron with linear electron trajectories is studied in the framework of linear and nonlinear theories. It is demonstrated that the clinotron effect is absent in the linear mode, since the amplification factor is maximized at zero angle between the beam and the surface of the slow-wave structure. In the large-amplitude mode, an obliquely incident beam, on the contrary, enhances the interaction efficiency. This is associated not only with the fact that partial layers of an obliquely incident beam propagate through the region where the HF field of the surface wave is largely localized, but also with weakening of nonlinear effects of bunching and energy exchange between the beam and the HF field. Comparative analysis of the efficiency of the clinotron effect in the modes of backward-wave oscillation and forward-wave amplification is performed.     

The oscillation adjustment in clinotron

Linear and nonlinear stages of the oscillation adjustment in a model of a source of millimeter-wavelength radiation (clinotron) are analyzed using the nonstationary theory of interaction in a system consisting of a thick electron beam and a backward wave. The duration of the transient process is studied as a function of the ratio of the working and starting currents and an angle of incidence on the surface of a slow-wave structure. It is demonstrated that the minimum duration of the process is reached in the vicinity of the optimal regime in which the beam is completely deposited on the surface of the slow-wave structure.     

Self-modulation of the output signal in clinotron

It is demonstrated that the self-modulation of the output signal in clinotron results from a delayed response of the distributed system of clinotron to the action of nonlinearity in the interaction of layers of a thick electron beam and high-frequency field. The effect differs from the self-modulation in a conventional O-type BWT, which is determined by the beam as a whole.     

W波段斜注管高频结构的设计和注波互作用模拟

斜注管是返波管的一种,其基本原理是将电子注稍微倾斜于慢波结构表面,通过改变电子注的倾角来优化有效互作用长度,达到更高的输出功率和效率.本文论述了斜注管的基本原理,对其冷特性进行了研究,初步设计了W波段斜注管慢波结构,并利用3D电磁模拟软件,对其注-波互作用进行了模拟,模拟得到20W的输出功率以及15GHz的带宽.     

基于透射体布拉格光栅频谱组束的研究

分析了透射体布拉格光栅实现两束不同波长光束频谱组束的条件.基于耦合波理论,推导了透射体布拉格光栅的衍射效率方程,获得了优化的组束设计条件,提出了使用凸透镜控制光束入射角的方法.建立了组束的理论模型,分析了光栅参数对衍射效率的影响.结果表明:最佳组束时,不同的光栅厚度须选择不同的光栅参数;在折射率调制和空间频率不变的情况下,随着光栅厚度的减小,谱选择性逐渐增大;随着光束发散的增大,光栅的衍射效率逐渐减小.     

On the electron flow movement in the decelerated wave field with exponentially positive-going amplitude

Initially homogeneous electron beam movement in longitudinal electric field of the decelerated electromagnetic wave is discussed. The wave amplitude exponentially increases along the electron’s trajectory. Comparison of solutions obtained numerically and analytically by disturbance method for small amplitude as a sixth approximation is made. It is shown that the approximate solution’s error is small when transit angle is small and the error starts catastrophically rising at some angle’s value. The problem is urgent for building the non-linear clinotron’s theory.     

光纤激光频谱组束的仿真研究

基于利用透射体布拉格光栅 准直透镜所设计的非相干组束方案,建立了光纤激光组束的理论模型.依据所建模型,对光栅的组束效果进行了分析.结果表明:最佳组束时,不同的光栅厚度须选择不同的光栅参数;随着光栅厚度的减小,满足最佳组束条件的空间频率和折射率调制将逐渐增大;在折射率调制和空间频率不变的情况下,随着光栅厚度的减小,角或谱的选择性逐渐增大;随着光束发散角和光谱宽度的增大,衍射效率逐渐减小.     

Theory of the clinotron: A grating backward-wave oscillator withinclined electron beam

A nonlinear theory of the clinotron, which is a modification of the backward-wave oscillator (BWO), is presented. The problem of electron-wave interaction is treated in a self-consistent formulation. Theoretical results are presented on starting conditions, steady-state oscillations, and temperature regimes. Potentials of the clinotron for further upgrading of efficiency and output power are examined     

面向小倾角近圆低轨卫星的DBF波束指向角研究

研究了DBF开环跟踪过程中面向小倾角近圆低轨卫星的波束指向角问题,为避免采用数据拟合进行轨道预测出现的奇点问题,文中引入改进的第二类无奇点根数代替经典开普勒根数,将地心惯性坐标系下的卫星位置速度转化为瞬时轨道根数。采用最小二乘法拟合得到平均轨道根数,以此为参数计算出航天器和中继星的位置,并给出了DBF波束指向角的计算流程。仿真结果验证了文中算法的正确性和有效性。     

无源微波遥感海上石油污染的研究

本文应用空气、油膜和海水组合体模型计算和分析了有效发射率随油膜厚度、工作频率和入射角变化的关系,提出了无源微波遥感海上石油污染的优选方案并成功地进行了航空微波遥感试验。     

光束准直性对星间相干光通信外差效率的影响

以本振光为高斯光,信号光为艾里斑分布为前提,建立了空间相干光通信系统外差效率的理论模型.分别在信号光垂直入射和存在角失配入射的情况下,对外差效率进行了仿真分析.结果表明,当光敏感面半径与高斯光束腰半径之比为1.53,且高斯光束腰半径与系统F数之比为0.8时,能得到最佳的外差效率为83.3%;信号光与本振光在光敏感面混频时的非准直对外差效率的影响较大,随着失配角的增大外差效率逐渐降低,几毫弧度的失配将使外差效率减小到50%以下.     

Estimation of the Optimal Maximum Beam Angle and Angular Increment for Normal and Shear Strain Estimation

In the current practice of ultrasound elastography, only the axial component of the displacement vector is estimated and used to produce strain images. A method was recently proposed by our group to estimate both the axial and lateral components of a displacement vector using RF echo signal data acquired along multiple angular insonification directions of the ultrasound beam. Previous work has demonstrated that it is important to choose appropriate values for the maximum beam angle and angular increment to achieve optimal performance with this technique. In this paper, we present error propagation analysis using the least-square fitting process for the optimization of the angular increment and the maximum beam steered angle. Ultrasound simulations are performed to corroborate the theoretical prediction of the optimal values for the maximum beam angle and angular increment. Selection of the optimal parameters depends on system parameters, such as center frequency and aperture size. For typical system parameters, the optimal maximum beam angle is around 10deg for axial strain estimation and around 15deg for lateral strain estimation. The optimal angular increment is around 4deg -6deg, which indicates that only five to seven beam angles are required for this strain-tensor estimation technique.     

体布拉格光栅光谱滤波器特性研究

高透过率、窄光谱带宽、高抑制比的滤波器件是提升光学系统光谱纯度的核心部件，也是近年来新型光学器件领域研究的热门方向。传统的滤波器件不能够同时满足透过率、光谱带宽以及带外抑制的要求，而文中研究的体光栅作为一种新型的光栅，衍射效率大于90%，光谱带宽在100 pm左右，并且拥有一定的角度滤波特性。依据耦合波理论，理论仿真了各个光栅参数（光栅厚度、折射率调制度、光栅周期、光栅倾角）对光栅衍射效率及光谱带宽的影响，定量地给出了参数影响的大小，为体光栅的设计提供了理论指导。设计了体光栅测试系统，通过实验验证了体光栅的衍射效率、光谱带宽、角度选择性，实验结果与理论较为符合，为体光栅的实际应用提供了实验数据支持。     

Effect of Mode Transformation in THz Clinotron

Extension of the theory of a clinotron is developed by use of the scattering matrix of an oversized T-junction on the ends of a slow wave system. The matrix contains elements corresponding to the transformation of slow grating modes into fast ones and vice versa. Those fast waves with low ohmic losses provide strong resonant properties of a clinotron even in the case of strong attenuation of the surface mode. Results of the theoretical simulation are compared with experimental ones and obtained dependencies explain strong resonances in sub-THz clinotrons.     

自由空间光通信链路最优束散角分析

讨论了FSO通信系统链路最优束散角问题。由空间光通信链路方程得出,减小束散角会增大通信链路裕量。在未对准误差情况下,深入分析偏移角、束散角与链路裕量之间的关系;假设未对准损耗是链路裕量的唯一影响因素的条件下,通过推导得出最大偏移角表达式,当未对准(偏移)角度取得最大值时对应的便是最优束散角。由仿真分析可知,偏移角度的增大导致系统接收光功率减小;对于该系统光束束散角处于1.6 mrad时便是最优束散角。该部分内容研究为对星地的上行和下行通信链路功率计算提供了理论支撑。     

激光扫描成像中旋转多面体的分析计算

对旋转多面体激光扫描成像系统作了理论描述及定量分析。为了保证扫描像点处于同一平面,将多面体置于成像物镜之前,当激光束以相对于光学系统光轴为2α角入射时,确定了入射光在多面体反射面上的位置、多面体中心转轴以及光学系统光轴三者之间的相对位置关系。推导了系统光学扫描角、扫描效率和入瞳漂移等参数的数学公式,分析了它们与入射光直径、入射角、多面体几何尺寸等因素之间的变化关系。结果表明,为减小系统的入瞳漂移和增大扫描效率,应以较小的入射角入射;进行系统设计时,若给定扫描角,扫描效率一般选择在0.4～0.7范围内较合理。     

Experimental investigations of thermally stimulated degenerate four-wave mixing

Results of experimental investigations aimed at testing efficiency-related aspects of thermally induced degenerate four-wave mixing in absorbing solutions are reported. The effects of fluorescence, read beam time delay, and forward beam angle variations are measured and shown to strongly influence the achievable thermal grating diffraction efficiency. In particular, a strong decrease of conjugation efficiency is observed as a function of increasing angle between the forward beams. Conjugate beam diffraction efficiencies as high as 17 percent were measured for the dye RhB in acetone. Based on our observations, we predict that still higher conjugation efficiencies will be feasible under optimal conditions with the thermal grating mechanism.     

Efficient Excitation of Hybrid Modes in a THz Clinotron

Journal of Infrared, Millimeter, and Terahertz Waves - Various regimes of hybrid, bulk-surface, modes being excited in the clinotron oscillator with a sheet electron beam and nonuniform grating...     

A nonstationary theory of the clinotron

Nonlinear equations for the analysis of the nonstationary operating mode of the clinotron are formulated. The linear stage of the transition to steady-state oscillations in the clinotron and the stability of the operating modes, which are found in the framework of the stationary single-mode theory, are considered. Complex dynamics of self-excited oscillations in the clinotron is revealed.